ssh-add1

Usage

Overview

ssh-add adds private key identities to the authentication agent, ssh-agent(1). When run without arguments, it adds the files ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519, ~/.ssh/id_ed25519_sk and ~/.ssh/id_mldsa44_ed25519. After loading a private key, ssh-add will try to load corresponding certificate information from the filename obtained by appending -cert.pub to the name of the private key file. Alternative file names can be given on the command line.

If any file requires a passphrase, ssh-add asks for the passphrase from the user. The passphrase is read from the user's tty. ssh-add retries the last passphrase if multiple identity files are given.

The authentication agent must be running and the SSH_AUTH_SOCK environment variable must contain the name of its socket for ssh-add to work.

The options are as follows:

-C

When loading keys into or deleting keys from the agent, process certificates only and skip plain keys.

-c

Indicates that added identities should be subject to confirmation before being used for authentication. Confirmation is performed by ssh-askpass(1). Successful confirmation is signaled by a zero exit status from ssh-askpass(1), rather than text entered into the requester.

-D

Deletes all identities from the agent.

-d

Instead of adding identities, removes identities from the agent. If ssh-add has been run without arguments, the keys for the default identities and their corresponding certificates will be removed. Otherwise, the argument list will be interpreted as a list of paths to public key files to specify keys and certificates to be removed from the agent. If no public key is found at a given path, ssh-add will append .pub and retry. If the argument list consists of “-” then ssh-add will read public keys to be removed from standard input.

-E fingerprint_hash

Specifies the hash algorithm used when displaying key fingerprints. Valid options are: “md5” and “sha256”. The default is “sha256”.

-e pkcs11

Remove keys provided by the PKCS#11 shared library pkcs11.

-H hostkey_file

Specifies a known hosts file to look up hostkeys when using destination-constrained keys via the -h flag. This option may be specified multiple times to allow multiple files to be searched. If no files are specified, ssh-add will use the default ssh_config(5) known hosts files: ~/.ssh/known_hosts, ~/.ssh/known_hosts2, /etc/ssh/ssh_known_hosts, and /etc/ssh/ssh_known_hosts2.

-h destination_constraint

When adding keys, constrain them to be usable only through specific hosts or to specific destinations.

Destination constraints of the form ‘[user@]dest-hostname’ permit use of the key only from the origin host (the one running ssh-agent(1)) to the listed destination host, with optional user name.

Constraints of the form ‘src-hostname>[user@]dst-hostname’ allow a key available on a forwarded ssh-agent(1) to be used through a particular host (as specified by ‘src-hostname’) to authenticate to a further host, specified by ‘dst-hostname’.

Multiple destination constraints may be added when loading keys. When attempting authentication with a key that has destination constraints, the whole connection path, including ssh-agent(1) forwarding, is tested against those constraints and each hop must be permitted for the attempt to succeed. For example, if key is forwarded to a remote host, ‘host-b’, and is attempting authentication to another host, ‘host-c’, then the operation will be successful only if ‘host-b’ was permitted from the origin host and the subsequent ‘host-b>host-c’ hop is also permitted by destination constraints.

Hosts are identified by their host keys, and are looked up from known hosts files by ssh-add. Wildcards patterns may be used for hostnames and certificate host keys are supported. By default, keys added by ssh-add are not destination constrained.

Destination constraints were added in OpenSSH release 8.9. Support in both the remote SSH client and server is required when using destination-constrained keys over a forwarded ssh-agent(1) channel.

It is also important to note that destination constraints can only be enforced by ssh-agent(1) when a key is used, or when it is forwarded by a cooperating ssh(1). Specifically, it does not prevent an attacker with access to a remote SSH_AUTH_SOCK from forwarding it again and using it on a different host (but only to a permitted destination).

-K

Load resident keys from a FIDO authenticator.

-k

When loading keys into or deleting keys from the agent, process plain private keys only and skip certificates.

-L

Lists public key parameters of all identities currently represented by the agent.

-P

When loading PKCS#11 or FIDO keys from a token, do not request a PIN. This will cause the operation to fail if the token requires additional authentication and has no other way to obtain it, such as a keypad or biometric reader.

-l

Lists fingerprints of all identities currently represented by the agent.

-N

When adding certificates, by default ssh-add will request that the agent automatically delete the certificate shortly after the certificate's expiry date. This flag suppresses this behaviour and does not specify a lifetime for certificates added to an agent.

-Q

Query the agent for the list of protocol extensions it supports. Note: not all agents support this query.

-q

Be quiet after a successful operation.

-S provider

Specifies a path to a library that will be used when adding FIDO authenticator-hosted keys, overriding the default of using the internal USB HID support.

-s pkcs11

Add keys provided by the PKCS#11 shared library pkcs11. Certificate files may optionally be listed as command-line arguments. If these are present, then they will be loaded into the agent using any corresponding private keys loaded from the PKCS#11 token.

-T pubkey ...

Tests whether the private keys that correspond to the specified pubkey files are usable by performing sign and verify operations on each.

-t life

Set a maximum lifetime when adding identities to an agent. The lifetime may be specified in seconds or in a time format specified in sshd_config(5).

-v

Verbose mode. Causes ssh-add to print debugging messages about its progress. This is helpful in debugging problems. Multiple -v options increase the verbosity. The maximum is 3.

-X

Unlock the agent.

-x

Lock the agent with a password.

Environment

DISPLAY, SSH_ASKPASS and SSH_ASKPASS_REQUIRE

If ssh-add needs a passphrase, it will read the passphrase from the current terminal if it was run from a terminal. If ssh-add does not have a terminal associated with it but DISPLAY and SSH_ASKPASS are set, it will execute the program specified by SSH_ASKPASS (by default “ssh-askpass”) and open an X11 window to read the passphrase. This is particularly useful when calling ssh-add from a .xsession or related script.

SSH_ASKPASS_REQUIRE allows further control over the use of an askpass program. If this variable is set to “never” then ssh-add will never attempt to use one. If it is set to “prefer”, then ssh-add will prefer to use the askpass program instead of the TTY when requesting passwords. Finally, if the variable is set to “force”, then the askpass program will be used for all passphrase input regardless of whether DISPLAY is set.

SSH_AUTH_SOCK

Identifies the path of a UNIX-domain socket used to communicate with the agent.

SSH_SK_PROVIDER

Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support.

Files

~/.ssh/id_ecdsa

~/.ssh/id_ecdsa_sk

~/.ssh/id_ed25519

~/.ssh/id_ed25519_sk

~/.ssh/id_mldsa44_ed25519

~/.ssh/id_rsa

Contains the ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted Ed25519, MLDSA44-ED25519 or RSA authentication identity of the user.

Identity files should not be readable by anyone but the user. Note that ssh-add ignores identity files if they are accessible by others.

Exit status

Exit status is 0 on success, 1 if the specified command fails, and 2 if ssh-add is unable to contact the authentication agent.